I don’t think so without them all running the server and receiving separate triggers, and we already know that isn’t working for your iPhone 6. Depending upon if it is fundamentally a trigger or execution issue, sending yourself a mail or message as another step could be used to trigger DND on the other devices.
You could add a step in Shortcuts or Zapier to write a file that is synced to your Macs that some local monitor (e.g. Hazel, Keyboard Maestro, folder action) could use to trigger a script to enable DND.
You could add SSH actions to your Shortcut to trigger a DND script directly on each Mac.
If you have a service that can receive a web request (e.g. Keyboard Maestro), you could also trigger with a URL call.